Thymocytotoxic antibodies in synovial fluid

Synovial fluid (SF), obtained from patients with juvenile rheumatoid arthritis (JRA), osteochondritis, traumatic synovitis and septic arthritis were tested for the presence of thymocytotoxic activity. Such activity, directed against guinea pig thymocytes, was earlier demonstrated in human serum and shown to be mediated by IgM antibodies and a heat labile factor, most likely complement. The cytotoxic activity was demonstrated in all SFs tested, and was abolished by either one of the following procedures: depletion of IgM by use of anti-IgM-antibody coated protein A-Sepharose, or heating to 56 degrees C for 30 min. Activity was regained when samples inactivated by these two procedures were recombined. The cytotoxic SFs produced similar distortion of cell volume distribution of the target thymocytes as previously has been shown with human serum. The findings indicate that the two cytotoxic activities are identical. In most cases the IgM levels and the cytotoxic activity were lower in SF than in normal serum. Although the material does not permit correlation of cytotoxic activity with specific joint conditions, a high SF cytotoxicity was noted in two out of four patients with JRA. The demonstration of IgM-associated thymocytotoxic activity is of interest both in connection with earlier observations of various specific antibodies in SF and in connection with speculations regarding local immune regulatory activity in the joint.